An outgoing chief constable will use his final day in office to warn social media outlets to play their part in protecting children.
Simon Bailey, head of Norfolk Police, will say introducing blanket end-to-end encryption will make it easier for offenders to go undetected online.
Mr Bailey, the National Police Chiefs' Council lead on child protection, calls the scale of abuse "overwhelming". He will speak at Anglia Ruskin University later. Mr Bailey will be speaking at a conference organised by the university's Policing Institute for the Eastern Region, as he retires after 35 years' police service.
He is due to say that social media companies have the ability to make uploading and sharing of indecent material "so much harder" but they "choose not to invest in the technology to eradicate it". "Unfortunately, the technology industry continues to put profit before safeguarding children," he will say.
"Facebook is already the most used platform for the sharing of indecent images and yet they are planning to wilfully blind themselves by introducing end-to-end encryption across their services. This will simply turn the lights off on our ability to effectively monitor this activity. "It is open to Facebook to change those plans."
Facebook's plans to roll out end-to-end encryption across its messaging services means only the sender and recipient will be able to read messages. While it travels, the message is scrambled to be unreadable, including by law enforcement. The only way to read the message is usually to get physical access to an unlocked device receiving it.
A spokesman for Facebook said: "End-to-end encryption is already the leading security technology used by many services to keep people safe from hackers and criminals." He said there was "no place" for child exploitation on its platforms and said it was "building strong safety measures into our plans" for the roll-out of encryption.
Mr Bailey's speech will describe the scale of abuse online as "simply overwhelming". The figures he is expected to cite include the National Crime Agency estimate, that there are between 500,000 and 850,000 people in the UK who pose a threat to children.
"Nine years ago the Child Exploitation and Online Protection Centre were responsible for coordinating 192 arrests in a year - police working in partnership with the National Crime Agency are now dealing with 850 offenders a month," he will say. "Our partnership has seen us safeguarding tens of thousands of young people, but the volume of offences continues to grow, the depravity is getting worse, and the victims are getting younger.
"The police and the NCA are doing everything we can but the onus now needs to be on the social media giants, who are still absolving themselves of responsibility."
